Volunteer potatoes in Michigan are surviving winters in increasing numbers, providing a bridge for late blight from one season to the next.
A new Michigan State University website helps estimate volunteer potato survival based on temperature, according to a grower e-newsletter.
Researchers blame the growing number of mild winters in Michigan for the greater risk from volunteer potatoes. Tubers of most potato cultivars begin to break down at 27 degrees Fahrenheit for one day. The model examines soil temperatures at depths of two and four inches between Nov. 1 and March 31 to make the estimates.
If soil temperatures dropped below 27 F at both depths for more than 120 hours between that time frame, then the chances of tuber survival is low. If soil temperatures dropped below 27 F at the two-inch depth but not at the 4-inch depth for more than 120 hours, then the chances of tuber survival is moderate. If the temperature didn't drop below the 27 F threshold for more than 120 hours at either depth, then the chances for tuber survival is high.
In areas where the risk from volunteers is high, researchers recommend scouting and implementing integrated pest management programs. They also recommend growers consider eliminating volunteers in adjacent non-potato cropland using appropriate registered herbicides.
The website was developed by Willie Kirk and Lee Dunslayger, Michigan State University Extension plant pathologists; Phil Wharton, University of Idaho plant pathologist; Kathleen Baker, Western Michigan University associate professor of geography; and Beth Bishop, MSU Enviro-weather coordinator.
SOURCE: Vicky Boyd, Editor, The Grower